Electrolytic production of metal alkyls



Jan. 5, 1965 K. ZIEGLER ETAL 3,164,538

ELECTROLYTIC PRODUCTION CF METAL ALKYLS Filed Aug. 3, 1961 6 Sheets-Sheet l Jan. 5, 1965 K. ZIEGLER ETAL 3,164,538

ELECTROLYTIC PRODUCTION OF METAL ALKYLS Filed Aug. 3, 1961 6 Sheets-Sheet 2 Fig. 1b

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9'1 5 I fig It I lllll/llllllllll/ INVENTORJI wt /MQW S Jan. 5, 1965 K. ZIEGLER ETAL 4 ELECTROLYTIC PRODUCTION OF METAL ALKYLS 6 Sheets-Sheet 3 Filed Aug. I5, 1961 E b K 51; P z 4 EE: ,P V A: I: 2 //n// n v I 32: .W R b .D 2 .h K Z? r B A Jan. 5, 1965 K. ZIEGLER ETAL ELECTROLYTIC PRODUCTION OF METAL ALKYLS 6 Sheets-Sheet 5 Filed Aug. 3, 1961 KDRL IIEGLER O O O O 0 O O O O O umm- LEHHWHL INVENTOR [W Z Jan. 5, 1965 K. ZIEGLER ETAL 3,164,533

ELECTROLYTIC PRODUCTION OF METAL mums Filed Aug. I5, 1961 6 Sheets-Sheet 6 BY w w United States Patent M 3,164,538 ELECTROLYTIC PRtJDUCTIflN 0F METAL ALKYLS Karl Ziegler, Kaiser Wilhelm Platz 1, Mulheim (Ruhr), Germany, and Herbert Lehmkuhl, Mulheim (Ruhr), Germany; said Lehmkuhl assignor to Karl Ziegler, Mulheim (Ruhr), Germany Filed Aug. 3, 1961, Ser. No. 129,009 Claims priority, applicaztiosnlgi7ermany, Aug. 11, 1960,

35 Claims. (or. 204-49) filed February 4, 1963; and Ser. No. 27,220, filed May' 5, 1960, abandoned in favor of the instant application.

Metal alkyl-s may be produced by electrolyzing complex aluminum-organic electrolytes at an anode of a metal corresponding to the metal of the metal alkyls which are to be produced.

A particular problem in the electrolytic production of such metal alkyls with the use of the complex aluminum-organic electrolytes is offered by the back de composition of the metal alkyls for-med from the anode metal by the metal deposited on the cathode. The following routes were suggested up to the present to avoid such back decomposition:

1) Use of a diaphragm inserted between the anode and cathode, preferably in connection with a certain flow of liquid electrolyte from the cathode space through the diaphragm and into the anode space.

(2) Using vacuum in the electrolysis, preferably high vacuum. In this method, the metal alkyl formed distills off before being able to be decomposed at the cathode. The use of a diaphragm may be dispensed with in this embodiment of the process.

In addition to the metal alkyls formed from the anode metal, free aluminum trialkyl is generally formed in the anode space during the electrolysis. This aluminum trialkyl likewise is prone to back decomposition with the metal deposited at the cathode in case of cathodic deposition of alkali metal. This interferes with the deposition of the pure metal and, instead, a mixture of, for example, sodium and aluminum will appear at the cathode or, in case of a larger amount of free aluminum trialkyl, only aluminum will be obtained in the cathode space. Here again, this undesirable back decomposition of the free aluminum trialkyl can be prevented by the two measures mentioned above.

Both of the hitherto known possibilities of ensuring a satisfactory course of the reaction show considerable disadvantages. The first method suffers from the complexity of any diaphragm arrangement and also from the fact that, in the presence of a diaphragm,.the dis- 3,164,538 Patented Jan. 5, 1965 In general, processes of this type are not favored in industry. This mode of operation is further complicated by the fact that, at the current densities used, small amounts of gaseous by-products are formed at the anode. These must be pumped oft continuously for maintaining the vacuum required. This increases the cost of operating the big pumps required in this case.

It is an object of this invention to provide a process for the productoin of alkyls of beryllium, magnesium, mercury or metals of main groups III to V of the Periodic Table by electrolysis of complex aluminum-organic electrolytes effected such that undesirable conversion of the metal deposited at the cathode is prevented in most simple manner and consequently the performance of the process is facilitated to an extremely great extent.

A further object of this invention is a highly preferred process for the electrolytic production of tetraethyl lead.

In accordance with the invention, a process for producing alkyls of beryllium, magnesium, mercury or metals of main groups III to V of the Periodic Table by electrolysis of aluminum-organic compounds comprises electrolyzing an electrolyte containing compounds of the general formula Me (AlR R') wherein R is an alkyl radical, R is an alkyl or an alkoxy radical or fluorine and Me is sodium, potassium or a mixture of sodium and potassium, on anodes of the metal whose alkyls are to be produced and on a mercury cathode.

In one preferred embodiment of the invention, the electrolysis is effected with an electrolyte which additionally contains compounds of the general formula AlR R' wherein R is an alkyl radical and R is an alkyl or alkoxy radical. For the case that R is an alkyl radical, i.e. additional free aluminum trialkyl compounds are present in the electrolyte, these compounds of the formula 'AlR may also be contained in the electrolyte in the form of their etherates or trialkylaminates. Furthermore, it is preferred that in the compounds of the general formulae given above the individual Rs are the same alkyl radicals. Where R likewise is alkyl radicals, it is further preferred that R and R likewise are the same alkyl radicals.

Particularly preferred electrolytes are those where, in

primary alkyl radical having up to 6 carbon atoms, R is a straight chain primary alkyl radical having up to 6 carbon atoms, a radical of the general formula OR' (wherein R" is an alkyl radical having preferably up to about 20 carbon atomsand especially up to 8 carbon atoms, or a cycloalkyl radical of fluorine, and Me is sodium or a mixture of sodium and potassium having a preferred potassium content up to about ticularly preferred of the compounds of the general formulae mentioned above and to be used as the starting electrolytes are complex compounds of the general formulae MeAlR MeAlR OR, NaF.AlR NaF.2AlR or mixtures thereof. In addition, further organic aluminum compounds, e.g. compounds which are not comblood in a complex'and having the formula AlR R' and/or etherates or trialkyl aminates thereof may be present in the electrolyte.

In accordance with the preferred embodiment for the production of alkyls of lead, an electrolyte mixture which contains potassium-aluminum-tetra-alkyl and potassiumfiuoride-aluminum trialkyl-complex is used. Thus, for the production of tetraethyl lead, an electrolyte'mixture which contains potassium-aluminum-tetraethyl and. potassium-fluoride-aluminum-triethyl-complex is used.

The process and consequently the construction of the electrolytic cells is extremely simplified by the use of the mercury cathode in accordance with the invention. Neither a vacuum nor a diaphragm is required. It has Par- . been found that alkali metal from the electrolyte is always primarily deposited at the cathode during the elect-rolysis. This alkali metal is immediately combined by the mercury cathode to form amalgam. In a surprising and completely unexpected manner, the cathodically deposited sodium metal combined as amalgam is in this form no longer prone to back decomposition with the aluminum-organic compounds present in the electrolyte and, moreover, does not enter into a reaction with the anodically formed metal alkyls as long as the alkali metal concentration in the amalgam does not increase to excessively high values. By the process of the invention, the cathodically deposited metal which, up to the present, complicated the overall process by secondary reactions is immediately converted into a form in which it is excluded from the reaction mechanism within the electrolyte under the reaction conditions so that special precautions for preventing commingling of anodic and cathodic products of the electrolysis are no longer required.

It is desirable for full economical utilization 'of the process of the invention to operate at high current densities. Due to these high current densities, a large amount of metal alkyl compounds is formed per unit time. It

was observed in a completely unexpected manner that this operation at high current densities is possible in accordance with the invention and can even be carried outwith unexpected advantages.

The high current densities result not only in the formation of a large amount of metal alkyls per unit time at the. anode, but also a large amount of alkali metal is simultaneously deposited per unittime at the cathode. If, forexample, sodium is deposited at the surface of the mercury cathode, sodium amalgam is formed thereon which is lighter in weight than mercury and, therefore, ha the tendency of remaining at the cathode surface. In view of the high current densities used, i.e. the large amount of sodium deposited per unit time, it was to be expected that a layer of relatively high sodium concentration would be formed at the cathode surface. However, since sodium amalgam which, for example, contains only 15% of sodium, like pure sodium, instantaneously reacts already with the non-complexed aluminum compounds in the electrolyte, it could be expected that the mercury cathode would not be usable at high current densities without special precautions. This assumption was still more backed by the fact that it is known from organic chemistry that'amalgams of higher sodium content react more vigorously and easier with organic compounds than does sodium alone.

In a completely unexpected manner, such undesirable back decomposition of the aluminum compounds contained in the electrolyte does not occur in the process of the invention even when using the high current densities set forth below. The process is, in fact, capable of .being operated up to very high current densities with the mercury cathode alone without any trouble. No difficulty whatever is encountered even with the thin Hg layers which are preferably used in practice and where the risk of such undesirable concentration of sodium is normally particularly great.

The process of the invention is, therefore, not only operable in the range of low current densities but also at high current densities. A range up to about 100 a./dm. is preferred, it being possible, however, to use still higher current densities if desired. The lower limit of current densities is at least 2 and preferably at least 5 a./dm. It may be desirable under certain circumstances to operate at current densities of at least a./dm. In many cases, the range from about 30 to 50 a./cm. is particularly preferred for carrying out the process.

The process of the invention is of particular importance for the production of metal alkyl compounds of the following metals: magnesium, mercury, aluminum, lead.

It has been found surprisingly that relatively high electrolysis temperatures may be used in the process of the invention. The sodium amalgam cathodically formed is stable towards the electrolyte even at temperatures of as high as about 180 C. Particularly preferred for carrying out the process of the invention is the temperature from about especially from about to about C. The electrolysis is also operable at temperatures of below 100 C. provided that the electrolyte is capable of being maintained in molten state, which, if required, may be achieved by adding even limited amounts of special solvents, especially ethers and tertiary amines or of aluminum trialkyl ether-ates or aluminum trialkylaminates.

The process is preferably directed such that an amalgam containing a maximum of about 1.5 wt. percent of sodium is formed at the cathode, i.e. the cathode metal is withdrawn batchwise or continuously from the elec trolyzer and replaced by mercury which is free from or poorer in sodium. When operating with higher percentages of sodium in the electrolysis, an amalgam will still be formed, but it will soon solidify and consequently give rise to difiiculties in transportation, especially when withdrawing the cathode metal continuously from the electrolyzer. The allowable limit of the sodium content in the still liquid mercury may increase with higher temperatures in'the electrolysis.

It is desirable for the economic performance of the process of the invention to free the sodium amalgam withdrawn from the electrolyzer at least partially from its sodium content and subsequently return it into the electrolysis. This regeneration of the mercury may be effected by different methods. For example, it is known to connect sodium amalgam as the anode and electrolyze it with the use of an inorganic electrolyte of, for example, sodium hydroxide. sodium iodide, and sodium bromide. Sodium metal is deposited in this case while the mercury is anodically freed from its sodium content.

The following process is preferred in accordance with the invention for the regeneration of the mercury from the sodium amalgam with simultaneous production of metallic sodium: the sodium amalgam is electrolyzed as the anode in a second electrolysis (secondary electrolysis) effected with the use of an electrolyte which contains complex compounds of the general formula MeAlR R' wherein Me is sodium or a mixture of sodium and potassium, R is alkyl radicals and R is hydrogen, an alkyl and/or alkoxy or aroxy radical. In this electrolysis, sodium metal is deposited at the cathode while the radical simultaneously evolved at the anode combines and dissolves sodium from the anode metal to form, for example, sodium ethyl. This resulting sodium compound immediately reacts with the free aluminum trialkyl or alkoxy or aroxy aluminum dialkyl simultaneously formed anodically to form'the corresponding complex compound so that, on an overall basis, the electrolyte does not undergo a change in its composition. However, care must be taken in this electrolysis that the sodium amalgam will not be impoverished excessively in sodium either at its surface (due to excessively high current densities) or throughout (by driving the electrolysis too far) since otherwise undesirable mercury dialkyl may be formed anodically in addition to sodium alkyl. It is preferred, therefore, to remove the sodium only partially from the amalgam. This is not of disadvantage for the reuse of the mercury, treated in the secondary electrolysis, in the "primary electrolysis for the production of metal alkyl since, in cyclic operation and with series-connected electrolytic cells, measures can be easily taken that the rate of sodium entering the mercury on the one side is the same as that of the sodium withdrawn from the other side whileleaving nevertheless a certain stationary basic sodium content in the mercury.

In a particularly preferred embodiment, this secondary electrolysis may be operated in form of a three layer process. In this embodiment, the sodium amalgam constitutes the lowermost layer on which the molten electroly-te is arranged in which, e.g. at a distance of a few millimeters above the amalgam surface, a wide-meshed net of insulating material, e.g. glass fiber or cellulose fiber fabric, is provided while the cathode is arranged at the electrolyte surface. The sodium which, at the preferred temperatures in excess of 100 C., is deposited in molten state at the cathode has a density which is somewhat higher than that of the electrolyte so that it sinks down in the electrolyte. It is, however, held up by the net of insulating material and thereby kept in suspension as the third layer in the electrolyte from which it can b withdrawn intermittently or continuously without any d-iificulty. Where sodium of particularly high purity is desired, such electrolysis can be carried out twice by refining the cathodic sodium from the first electrolysis once more in a second electrolysis. This may be eiiected in a single cell in which a second net of insulating material with a superimposed sodium layer is arranged between the cathode and anod of the process described above. The space below and above this middle sodium layer is occupied by electrolyte so that, as the current is flowing, sodium is first separated as raw sodium from the amalgam in the middle layer and thence deposited as sodium of highest purity in the upper layer.

Secondary electrolysis as is described above, is dis closed and claimed in application Ser. No. 299,689, filed July 31, 1963, by the applicants herein and another, and assigned to the 'assignee hereof.

During the electrolysis effected in the manner disclosed in our patent specifications mentioned above, the metal alkyl compounds are formed from the anode metal in addition to the decomposition products of the electrolyte. In this procedure, the subsequent separation of the resultant reaction mixture may ofier difficulties especially in those cases where the boiling points of the metal alkyls formed and those of the aluminum-containing decomposition products of the electrolyte are close together such that distillation to separate the compounds is impossible or only operable with dificulties. A process which overcomes this difiiculty is disclosed in our co-pending patent applications 792,614 and 792,467. In this process, the anodic reaction products obtained in the electrolysis and consisting of a mixture of the formed metal alkyl with free aluminum trialkyl are reacted with complex compounds of the general formula MeAlR OR either as early as during the electrolysis of an electrolyte of the general formula MeAlR or subsequently to the electrolysis outside of the electrolytic cell. Thereby, the free aluminum trialkyls are converted into the alkalialuminum tetraalkyl compounds while free alkoxy aluminum dialkyl compounds are simultaneously formed. The separation of the metal alkyls from these compounds is then easily possible, e.g. by distillation.

Thus, it may be preferable for the process of the invention to have also recourse to the processes described in our co-pending patent applications 792,614 and 792,467 in those cases where difliculties are encountered in separat-ing the formed metal alkyls and the aluminum-containing decomposition products of the electrolyte. Examples of this are the lead tetraalkyls and in particular lead tetraethyl. This additional operational measure may be unnecessry in other cases. If, for example, magnesium dialkyl which is non-volatile is produced, separation of the resultant mixture of magnesium dialkyl and aluminum trialkyl is easily possible after or during the electrolysis by distilling off the volatile aluminum trialkyl, especially in vacuo. However, the vacuum needs not be as high in this case as in the processes hitherto described so that electrolysis in vacuo is operable without any difliculty with the use of a mercury cathode. Treatment of the formed electrolysis products for the purpose of reacting the aluminum-containing decomposition products is, of course, also unnecessary in the production of aluminum trialkyl.

It is desirable for the economic performance of the process of the invention that the decomposition products of the electrolyte formed in the electrolysis be regenerated and recycled for reuse. This is achieved without difficulties in case of the aluminum-containing decomposition products which are obtained at the anode in the electrolyte. As a side reaction, a gaseous decomposition product is evolved in limited amount at the anode by decomposition of hydrocarbon radicals. This undesirable decomposition does not occur at very low current densities, but becomes then more pronounced as the current density increases. However, when eilecting the process of the invention in a vacuum cell, it appeared surprisingly that this formation of undesirable gaseous reaction products decreases again as the current density is further increased to the range of high current densities preferred in accordance with the invention instead of increasing in an undesirable manner as might have been expected.

For improving the economy of the process, it is desirable that the aluminum-containing decomposition products of the electrolyte formed during the electrolysis be reconverted into complex aluminum compounds which are used as electrolyte or as a treating agent during the electrolysis. Thus, for example, free aluminum trialkyl is treated with an alkali metal, especially sodium, hydrogen and olefins to be reconverted into the alkali metal aluminum tetraalkyl complex compounds which may find use as the electrolyte during the electrolysis in the process of the invention. A reaction of this kind is, for example, described in our Patent 2,826,598. Free alkoxy aluminum dialkyl compounds are likewise treated with, for example, sodium, hydrogen, and olefins to be reconverted into the sodium alkoxy aluminum trialkyl complex compounds which may be used as both the electrolyte or as an addition during the electrolysis to eliminate undesirable free aluminum trialkyls or for the treatment of the electrolysis products outside of the electrolytic cell. Process for the regeneration of such aluminum complex compounds from the aluminum-containing decomposition products of the electrolyte are described in our co-pending patent application 792,614. All of the measures described in this specification may be applied in the process of the invention with the advantage according to the particular case.

In this manner, cyclic processes for the electrolytic production of metal alkyls can be carried out in accordance with the invention. In this embodiment, the elec trolytes containing compounds of the general formula Me(AlR R') are subjected to electrolysis on anodes of the metal whose alkyls are to be produced and a mercury cathode. The sodium amalgam formed at the cathode is preferably withdrawn continuously from the electrolytic cell prior to solidification and, in a second electrolysis (secondary electrolysis) freed at least partially from its sodium content and returned into the primary electrolysis to produce the metal alkyls. At the same time, the metal alkyls formed and the aluminum-containing decomposition products of the electrolyte are separated from the electrolyte and separated from each other. Following this, the aluminum containing decomposition products together with the sodium from the secondary electrolysis of the sodium amalgam are treated with hydrogen and olefins to be reconverted into the electrolyte compounds consumed during the electrolysis and returned into the primary electrolysis. Except for unavoidable losses of aluminum-organic compounds, the only fresh materials constantly required in this embodiment of the process are the starting materials for the production of metal alkyls, i.e. the metal whose alkyls are to be produced, hydrogen and the appropriate olefins. All of the further adjuvants used in the reaction are recycled within the process itself. However, other cyclic processes are also operable. Thus, for example, one may start with an electrolyte which contains the compounds NaF.2AlR (1:2 compound) and NaF.AlR (1:1 compound). Aluminum trialkyl is evolved in the electrolysis in addition to the metal alkyl this electrolyte.

produced from the anode metal. This aluminum trialkyl is immediately combined by the 1:1 compound present in the electrolyte to form the 1:2 compound so that separation of the metal alkyl formed from the anode metal is possible without any difficulty. A portion is intermittently or continuously withdrawn from the electrolyte, and 1:2 compound at a rate at which the 1:1 compound was converted into the 1:2 compound during the electrolysis is treated with sodium, hydrogen and olefins to form a mixture of 1:1 compound and NaAlR This mixture is then added to the electrolyte. Here, the 1:2 compound is immediately formed from the anodic electrolysis product R AlF and the sodium aluminum tetraalkyl so that the starting mixture of 1:1 and 1:2 compound is re-forrned in the-electrolyte.

The process of the invention is operable at relatively low terminal voltages of, for example, about 1 to 5 volts and preferably of about 1.5 to about 3 volts.

The selection of the electrolyzer and the conditions maintained therein may be adapted to the specific requirements of the particular case. A particularly simple case is, for example, the production of aluminum triethyl or magnesium diethyl. These are metal alkyls which are lighter in weight than the electrolyte used during the primary electrolysis, i.e. the metal alkyls formed rise in upward direction and may, since they do not mix with the complex electrolytes, be withdrawn as a separate layer from the top. The production may, for example, be carried out as follows:

The electrolyzer is a simple heatable cylindrical vessel containing at the bottom mercury as a layer of, for example, l to 2 cm. depth. The molten electrolyte such as, for example, sodium aluminum tetraethyl or a mixed electrolyte of higher conductivity comprising sodium and potassium aluminum tetraethyl is charged on top of the mercury. A bundle of aluminum or magnesium plates disposed vertically at a small distance is immersed in These plates may, for example, have a thickness of about 2 to 3 mm. Their distance is about 2 mm. This arrangement of the plates is preferable because small amounts of gases are evolved at the anode during the electrolysis. These gases may easily escape in an upward direction in the interspaces of the system of vertical plates while, in case of a solid metal block,

.they would cover the metal at the bottom face and consequently interrupt the current flow. The bundle is approached to the mercury leaving a gap of a few millimeters. Then the electrolysis is effected using, for example, a terminal voltage of about 2 volts and current densities from to a./dm. (these conditions applying to the case of sodium aluminum tetraethyl as the electrolyte and being still more favorable when using the mixed electrolyte mentioned above). The bundle of plates dissolves from the lower edges. The mercury converts into sodium amalgam of gradually increasing con centration and aluminum triethyl accumulates at the surface of the electrolyte layer in case of aluminum anodes while a mixture of the composition which is likewise liquid is obtained in case of magnesium anodes. This mixture is exactly a loose complex compound which may subsequently be separated by heating in vacuo into magnesium diethyl left as the residue and aluminum triethyl which distills. When using aluminum anodes, 4 molecules of aluminum triethyl are obtained in usual manner for three current equivalents. One of these molecules was newly formed from the aluminum metal while three of them were formed from the electrolyte as aluminum-containing decomposition products. Distinct and smooth separation into layers occurs between aluminum triethyl and electrolyte. In continuous processes, sodium aluminum tetraethyl is fed and the aluminum triethyl formed is withdrawn continuously. Similarly, the amalgam must be removed intermittently or continuously and replaced by fresh mercury. The amalgam is then passed into the secondary electrolysis described above while three of the four molecules of aluminum triethyl formed return into the regeneration of the electrolyte of the primary electrolysis. The sodium to be recovered cathodically from the secondary electrolysis is available for this regeneration and is reacted with hydrogen to form sodium hydride which is added to the aluminum triethyl and then treated with ethylene. Any back decomposition of aluminum triethyl in contact with the sodium amalgam with precipitation of aluminum will not occur even in case of extended periods of contact and high temperatures of, for example, to C. In a modification of the process, the resulting aluminum triethyl may be distilled out of the electrolytic cell under a slightly reduced pressure. The particularly high vacuum formerly required is, of course, no longer necessary. The particular simplicity of the arrangement just described is due to the fact that the organometallic compounds formed in the cases described above are lighter in weight than the electrolyte in which they rise in upward direction.

In other cases, e.g. in the case of tetraethyl lead, the metal alkyl formed may sink down in the electrolyte. If no special precautions would be taken, the cathodic mercury surface would soon be covered by the liquid metal alkyl with consequent interruption of the current flow in the electrolyte. In this case, a minor modification of the process is necessary. Moving electrolyte liquids are used in the electrolytic cell in such cases, the operation with flowing electrolytes being such that the electrolyte flowing over the mercury surface entrains the metal alkyl compounds falling down. These compounds will then sink to the bottom in a more quiescent part of the apparatus where the mercury can no longer be covered.

In accordance with a preferred embodiment of the invention for the electrolytic production of metal alkyls an electrolyte system is used which is composed exclusively or predominately of potassium-aluminum tetralower alkyl and p0tassium-fluoride-aluminum tri-lower alkyl-complexes. In the case of the production of the corresponding metal ethyl compounds, the electrolyte system should be composed exclusively or predominately of potassium-aluminum tetraethyl and potassium-fluoridealuminum triethyl complexes. With the use of this electrolyte, a mixture is produced in the electrolysis which consists of potassium-aluminum tetraethyl and potassiumdialuminum hexaethylfluoride with the metal ethyl compound greatly facilitating the separation of the metal ethyl from, the electrolyte. This advantage is of particular importance with anode metals such as lead or mercury, only with aluminum it does not weigh so heavily.

In accordance with this embodiment of the invention, it is possible to initially charge the cell with a mixture of K[Al(C H )4] and K[Al(C H F] and to conduct the electrolysis until the complex or compound 2 5)3 has been extensively converted into the complex K 2 z s) 6F] with a corresponding decrease in the content of the potassium-aluminum tetraethyl.

Alternately, the cell may be initially charged with an electrolyte which contains in addition to the potassiumaluminum tetraethyl and potassium-aluminum-triethylfluoride, potassium-dialuminum-hexaethylfluoride or even consists exclusively of potassium-aluminum-triethyl and potassium-dialuminum-hexaethylfiuoride provided that in the latter case a portion of the electrolyte containing tetraethylead is continuously removed and fresh electrolyte, as for example regenerated electrolyte, is continuously added so that the composition of the electrolyte will remain substantially constant.

The regeneration of the electrolyte for recycling may be effected in accordance with Belgian Patent 593,386 which involves the reaction of an alkali hydride and ethylene. This regeneration may preferably be effected with the use of sodium compounds in place of potassium compounds, as for example, sodium hydride. This will result in the formation of the sodium complex, as for example sodium aluminium-triethyl hydride or sodium aluminum tetraethyl which may be converted into the corresponding potassium compounds by reaction with potassium amalgam which results in an exchange of the potassium ion. The potassium-aluminum-organic complex compound formed may thus be recycled to the electrolyte and the accumulated sodium amalgam may be utilized in a secondary electrolysis in accordance with the process of Belgian Patent 590,574 for obtaining sodium, on the one hand, and mercury on the other. The sodium may be used again as a starting material for the regeneration step to the sodium-aluminum organic complex compounds.

The advantageous use of the potassium compounds was completely unexpected as for example in the electrolytic production of tetraethyl lead, temperatures above about 140 C. should be avoided and it is preferable to Work at temperatures between about 80 and 100 C. The potassium-dialuminum-hexaethylfluoride, however, has a melting point of 134 C. which would indicate the use of the undesirable high temperatures in the process. Quite surprisingly, however, the melting point of the potassiumfluoride complex may be so substantially lowered, through the admixture of the potassium-aluminum-tetraethyl, that a trouble-free operation of the electrolysis in the preferred lower temperature range is possible.

The potassium-containing electrolytes as used in accordance With this preferred embodiment of the invention furthermore have a considerably higher electrolytic conductivity than the corresponding sodium compounds.

The use of the potassium-containing electrolytes, in accordance with this preferred embodiment of the invention, allows a much more efficient and economical recovery of the formed metal alkyl for example tetraethyl lead as the tetraethyl lead is much less soluble even at the relatively high temperatures prevailing in the electrolysis cell in the potassium-containing melt than in the corresponding sodium-containing electrolyte. Thus, when operating at electrolysis temperatures between about 80- 120 C., the solubility of the tetraethyl lead in the system containing the sodium compounds is approximately between 8-12% so that it is necessary to cool the electrolyte to room temperature, or even below, in order to lower the solubility even to about 4%. In surprising contrast thereto, the solubility of the tetraethyl lead in the mixture of the potassium-aluminum-tetraethyl with the potassium-dialuminurmhexaethylfiuoride at a temperature between about 80100 is only about 2%. Thus, the tetraethylead will separate directly in the electrolysis cell at the electrolysis temperatures and may be directly drawn off. A cooling to room temperature, therefore, is not necessary and should not be effected when considering the melting temperature of the potassium compounds.

For efficient operation, it is necessary to remove even a small residue of the tetraethyl lead from the electrolyte. When operating in accordance with the abovepreferred embodiment of the invention with the use of the potassium-containing electrolyte, this, removal may be very simply, quickly, and eificiently achieved by means of a vacuum distillation. The residue of the tetraethyl lead may be distilled oif in this manner without any separation of aluminum triethyl.

The sodium complex, i.e. NaF.2Al(C H is, on the other hand, thermally much more unstable. Therefore, when attempting separation of the tetraethyl lead from this sodium complex by distillation, the distillate always contains split-off aluminum triethyl.

When operating this preferred embodiment of the invention, using potassium-aluminum-tetraethyl and potassium-aluminum-triethylfluoride as the electrolyte, the theoretical limit of the molar ratio of these components is 1:1. With the passage of 1 Faraday of current through this electrolyte between the metal anode for example lead anode and mercury cathode, the electrolyte is theoretically converted to Further electrolysis is not possible as a practical matter as free aluminum triethyl would be formed. The final state of the electrolysis, without this formation of free aluminum triethyl corresponds to a content of 21.8% of tetraethyl lead in the electrolyte.

Operation with a complete conversion of the potassium-aluminum-tetraethyl is not preferable due to the high melting point of the potassium-dialuminurn-hexaethylfluoride complex, as mentioned above, which necessitates operating at a high temperature to maintain the same in a liquid phase. It is, however, possible to operate with this high temperature and to still avoid decomposition of the tetraethyl lead if the electrolysis is operated with a short time of stay of the electrolyte containing the formed tetraethyl lead in the cell, and if the tetraethyl lead is quickly separated from the electrolyte passed out of the cell. This may be done, for example, by injecting the entire electrolyte mixture coming out from the cell into a distillation column operating under vacuum and heated, for example to 150160 C.

It is, however, more appropriate to operate at lower temperatures which is permitted by the effect of the potassium-aluminum-tetraethyl and lowering the melting point. For this purpose, it is preferable to operate with an electrolyte which contains about 0.43 to 0.18 mol of the potassium-aluminum-triethylfluoride per mol of potassium-alurninum-tetraethyl. With the use of such an electrolyte, a current quantity suflicient to convert the potassium-aluminum-triethylfluoride into the potassiumdialuminum-hexaethylfluoride will produce an end produce having a melting point between about 68 and 100 C. and with a content of 6.8 to 13.3% tetraethyl lead.

When operating the cell with an electrolyte which contains the potassium-dialuminum-hexaethylfluoride, and keeping the content of this complex constant, or substantially constant, it is also preferable to maintain a quantity of the potassium-aiuminum-tetraethyl so that the melting point of the electrolyte remains within the limits of Gil-100 C.

When operating under the optimum conditions as indicated, around -85% of the tetraethyl lead may be directly separated from the electrolyte liquid as a heavy lower layer and may be drawn off at a suitable place from the electrolysis cell. It is also possible to pump the electrolyte, including the formed tetraethyl lead suspended therein, into a storage vessel and back again into the cell and to permit the tetraethyl lead to settle in the storage vessel. The slight residual content of the tetraethyl lead remaining dissolved in the electrolyte is, as previously pointed out, preferably driven off through a continuous distillation under decreased pressure of, for example, at most a few torr which in turn has a liquid temperature of 80-120 In place of distillation, the tetraethyl lead may also be separated by extraction, as for example described in detail in French Patent 1,208,435.

All the essential advantages or" this preferred embodiment of the invention may still be obtained if the electrolyte contains, in addition to the potassium compound a certain content of sodium compound. A noticeable decrease in the very favorable results obtained with the use of the potassium compounds only occurs when ratio of gram atoms of sodium to gram atoms of potassium becomes greater than about 1:10.

A number of embodiments of the equipment may be used for carrying out the process of the invention on a commercial scale. Described hereinafter are a number of these embodiments which are particularly suited for the electrolytic production of tetraethyl lead but which may be adapted to the production of othermetal alkyls without difiiculties.

In the drawings:

FIG. 1a is a cross-sectional view, in elevation, of an electrolysis cell suitable for practice of the invention;

FIG. 1b isa plan view of an element of the cell shown in FIG. 10;

FIG. 1c is a cross-sectional view of the element shown in FIG. lb, taken along the section line lc-lc indicated in FIG. 112;

FIG. 2 is a cross-sectional view, in elevation, of acell wherein means are provided for continuously replenishing the lead consumed at the anode;

FIG. 3a is a cross-sectional View, in elevation, of a device corresponding to that shown in FIG. 2, but having an alternative means for continuously replenishing the lead anode and further employing a plurality of anodes;

FIG. 3b is a cross-sectional view taken along the section line 3b3b indicated in FIG. 3a;

FIG. 4a is a cross-sectional view, in elevation, of another embodiment of the cell;

FIG. 4b is a plan view, in cross-section, with portions of the device broken away, of the cell shown in FIG. 4a;

FIG. 40 and FIG. 4d are end elevation views illustrating the manner in which the lead anodes are arranged and supplied in the cell shown in FIG. 4a;

FIG. 5a is another embodiment, in cross-section and in elevation, of a cell suitable for practice of the invention;

FIG. 5b is a cross-sectional plan view of the cell shown in FIG. 5a, and taken along line Sta-5b in FIG. 5a; and

FIG. 50 is an end elevation View, in cross-section, of

the device shown in FIG. 5a.

FIG. 1 shows an electrolytic cell which may be used to an order of magnitude of as high as about 500 amps. The system comprises a lower vessel A having a cylindrical outer shell, the constructional details being derivable from the cross-sectional view shown in the drawing, especially FIG. 1a. This vessel receives the bulk of the electrolyte during the electrolysis. Collected in the lower narrowed section is the heavy metal alkyl layer which may be drained from time to time through the two valves H. The constriction of the vessel A in downward direction permits the metal alkyl layer to be cooled separately without a substantial reduction in temperature of the electrolyte. For reasons of current economy (increase in conductivity) the temperature in the electrolysis zone proper preferably ranges above 100 C. However, the finished metal alkyl collecting at the bottom should be maintained at a temperature of not more than about 70 C. if possible.

The vessel A is closed on top by a dish-shaped cover B, the constructional details of which may likewise be seen from the drawing, especially FIG. 1b. The dish B is recessed in the center and has a perforated flange. This dish is filled with mercury which is supplied or withdrawn at the two points indicated by Hg and the arrows .through bores in the flange of the dish. The dish is lowered during the electrolysis and that it permits the necessary fine adjustment. Provided in the center of the entire arrangement is the stirrer R.

The bottom face of the lead block is at a distance of a few millimeters above the mercury. As current is passed through, the droplets of metal alkyl formed at the bottom face of the block'are entrained by the flow of the the mercury and too high in the central hole.

electrolyte when the stirrer is in operation. In this manner, the lead and mercury surfaces are kept free for the passage of current. The gas bubbles collecting at the lead are likewise removed in this manner. The electrolytic cell is adapted to be externally heated or, in case of high current densities, cooled at the outer cylindrical jacket by suitable means. The diameter of the mercury-containing annular part of the dish B is, for example, about 30 to 40 cm. The cell may, however, be enlarged. Moreover, it is easily possible to arrange a plurality of assemblies B-l-C on a larger common lower vessel. The diameter cannot be enlarged at will because otherwise the flow velocities would be too low at the outer periphery of It will be always possible with reasonable dimensioning to find a stirring velocity which keeps the stirrer sufiiciently in motion While leaving the mercury completely unaffected so that its surface is practically stagnant. The cell is preferably connected together with a second cell in which the mercury is the anode so that it looses again its sodium. The mercury is then recycled between the two cells.

Another embodiment which may be combined with the device shown in FIG. 1 is illustrated in FIG. 2. In case of the cell construction of FIG. 1, the problem of continuously supplying the dissolving lead is not dissolved. If the lead block first suspended is consumed, the air-sensitive electrolyte must be removed, the cell rinsed and be taken again into operation after having suspended a new lead block. Shown in FIG. 2 is the upper part of a system which permits continuous operation. Represented in the middle of FIG. 2 is again the dish B having the same significance as in FIG. 1. The lower vessel A is only indicated. The lead block (Pb) is arranged above the dish in aseparate cylinder Z which is adapted to be externally cooled (at K). The system is closed at the top by the cover D which supports in the center a heavy threaded hollow bolt 5 which is adapted to be rotated from outside of the entire system by means of a wrench. This bolt bears the lead block Pb, the bore of which is provided with corresponding mating threads. The inner wall Z and the threaded bolt S are coated with a lubricant which is stable up to about 400 C.

When taking the system into operation, the lead block suspended at the spindle is first inserted into the apparatus. During the electrolysis, the lead block is lowered by turning the spindle. In doing so, care is taken that the lead block is not able to follow the rotary motion of the spindle so that it slowly lowers as the spindle is rotated at an appropriate speed. In this manner, feeding of the lead at the rate of its dissolution is very easily accom plished.

If a sufiicient part of the lead has disappeared, molten lead is poured through the upper opening in the cover D. The lubrication at the Walls and at the spindle prevents the lead from adhering to the metallic parts (steel) at K and S, and any quantity of lead may be dissolved below and replenished on top so that the entire system operates fully continuously.

A further alternative is illustrated in FIG. 3. The systerns shown in FIGS. 1 and 2 are somewhat clumsy due to the high weight of the metal block to be introduced. FIG. 3 shows a further embodiment where the lead block is subdivided into a series of a total of 18 individual lead cylinders of smaller diameter.

FIG. 4a again shows a longitudinal section of the electrolytic cell which in this case has the shape of a parallelepiped (at least in the upper part) rather than of a round cylinder. This apparatus also has in the center a dish-shaped container B for the mercury which again is introduced at one end and withdrawn at the other side. in this trough of rectangular cross section, there are arranged parallel to the flow direction of the mercury, a plurality of insulating bars G consisting, for example, of edgewise mounted strips of glass plates, one of which is indicated at G in FIG. 4a, and which are better to be seen in the plan view shown in FIG. 4b.

Shown in FIG. 4c is the manner how thick plates of lead (Pb) are placed on these bars in operation. It is possible to occupy the full width of the electrolytic cell by such lead plates which support one another. The lead plates are tapered like a roof at their upper ends. The replenishment of consumed lead is effected with similar plates which additionally are provided at their lower ends with a cavity corresponding to the taper at the upper ends.

Indicated in FIG. 4d is a number of such lead plates in various phases of dissolution. As the current passes through, an arching is developed in the interspaces between the supporting bars. However, the lowermost parts of theplates supported by the bars are also attacked laterally so that the lead descends continuously. New plates are put on timely. As may be seen from the right hand part of FIG. 4d, the plate can dissolve completely with out the opportunity being given that any, loose residual parts may be formed intermediately, drop into the mercury and give rise toshort circuits. If the expedient of roof-shaped tapers would not be used, the last parts of the lowermost lead disc would finally form only thin lead foils which, as experience has shown, never dissolve completely uniformly so that the risk of the formation of loose lead residues between the bars would exist. This, in turn, would provide the possibility of breakdowns if the last residues of the lower disc dissolve and the lower face of the replenishing disc follows down.

The distance between the mercury and the bottom faces of the lead discs is again several millimeters to centimeters. It can be easily understood that, with the principle described above, it is possible to arrange on a horizontally arrangedmercury cathode of any size in a fully reliable manner lead anodes which requireno special measure for replenishing the lead except for a timely setting up of replacement pieces. It also can be easily achieved with this system that the lead simultaneously functions as an upper air seal for the entire setup. Thus, this embodiment is particularly suited for commercial cells which consequently become very similar in their middle part containing the mercury to the conventional amalgam cells of the alkali chloride electrolysis.

FIG. 5 shows a further embodiment of a cell which is particularly suited for the commercial production of lead tetraethyl at a rate of l to 2 metric tons/day. The cell is particularly easy to operate with respect to the feeding of fresh lead. Arranged in the middle is a layer of flowing mercury (at Hg). In this section, the setup is completely identical to the conventional amalgam cells used in the electrolysis of aqueous sodium chloride solutions by the amalgam process. Thus, in operation, the mercury runs in form ofa thin film from the left hand side to the right hand side over a very slightly inclined metal plate of several meters in length. The amalgam is withdrawn at the right hand side. Means for withdrawal are not shown in the drawing. The mercury cathode is supported by an elongated base member of trough-shaped cross section which contains a larger amount of electrolyte and wherein a circulation may be produced by a longitudinal partition wall in the middle and a series of stirrers,

the circulation being such that the electrolyte rises at one side of the device, then fiowsthrough the interspace between the mercury and the anodes and descends on the other side. Any further information as to the formation the setup is fully continuous.

. anodes.

of tetraethyl lead may be derived from a comparison with the other figures.

Particularly characteristic of this electrolytic cell is the manner in which the lead anodes are arranged. Here again, the lead anodes consist of individual square-shaped discs which, however, are suspended on special attachments such that they are able to roll from left to right following the inclination of two supporting runners S. When providing the first charge, the lead pieces decrease in height from left to right. Provided at both ends of the setup are inlet and outlet locks, the construction of which is not described in detail at this place and which makes it possible to remove at the right end an attachment with a small lead residue which may still be present and to insert a new disc at the left end into the gap becoming free. It can be achieved with this device which is very simple in construction that with slow motion of the, total of discs from left to right the dissolution of the lead at the lower ends is just compensated by the amount of descending on the inclined plane so that the distance between the lead and mercury which should be a few millimeters will always be constant. The operation of It is particularly convenient due to the fact that the only measures necessary for attendance must be effected at two points only (left and right) and it is unnecessary to service the cell over the total cross section with respect to the replenishment of consumed lead. The entire upper part of the setup is capable of being perfectly sealed against the atmosphere. Feeding into the locks and withdrawal from the locks is restricted to a very small spatial area which can be easily designed as an inert gas lock.

The following examples are given by way of illustration and not limitation.

Example 1 A mixed electrolyte comprising of potassium aluminum tetraethyl and 50% of sodium aluminum tetraethyl is subjected to electrolysis at 100 C., effected in the apparatus shown in FIG. 1 with the use of lead A current density of a./dm. can be maintained by a terminal voltage of 7.5 volts. 166 grams of NaAl(C H which is equivalent to the amount of current passed through are allowed to flow into the electrolytic cell per 26.8 ampsxhours. The anodically formed mixture of 81 gms. of lead tetraethyl and 114 gms. of aluminum triethyl which is sparingly soluble in the electrolyte collects in the lower part of the apparatus at H and may there be drained from time to time. The sodium amalgam formed at the cathode is continuously withdrawn at Hg when having reached a concentration of 1% Na. The amalgam is freed from Na except for 0.2% Na in a secondary cell and the amalgam which is poor in sodium is continuously returned into the electrolytic cell.

Obtained per 26.8 amperesxhours are 81 grams of tetraethyl lead and 114 grams of aluminum triethyl (corresponding to 100% of the theory) and 23 g. of sodium dissolved in the mercury.

The separation of tetraethyl lead and aluminum triethyl may be effected in accordance with the process of our co-pending patent application 792,467 by reaction of the mixture with a suitable sodium alkoxy aluminum triethyl compound and subsequent distillation.

Example 2 The procedure is as described in Example 1 except that an electrolyte comprising of sodium aluminum tetraethyl and 10% of sodium-decyloxy-aluminumtiiethyl is used; Sodium-dccyl-oxy-aluminum triethyl is allowed to flow in at a rate to be adapted to the amount of current I and a bath temperature of 100 C. The residue consists of pure decyloxy aluminum diethyl which may be reacted with NaH and ethylene at 190 C. and an ethylene pressure of 10 atmospheres to form sodium decyloxy-aluminum triethyl which may be used for another electrolytic operation.

Regarding the Na amalgam, the procedure is such that part of the amalgam is continuously withdrawn at a sodium content of 1.5% in the mercury and replaced by amalgam poor in Na (0.2% of sodium).

Example 3 Electrolysis is effected with an electrolyte of the composition NaF.2Al(C H in the apparatus shown in FIG. 1 using an aluminum anode. Molten sodium aluminum tetraethyl is allowed to flow into the cell at a rate which corresponds to the amount of current passed through. The electrolysis temperature is 150 C. The terminal voltage required at a current density of 20 a./dm. is 3.5 volts. The anodically formed aluminum triethyl which is sparingly soluble in the electrolyte separates as the upper layer if the zones of slower flow are arranged in the upper part of the apparatus in this case. Aluminum triethyl in amount of 152 grams of which 38 grams are freshly formed are obtained per 26.8 amps. hours.

As regards the Na amalgam, the same procedure is applied as in Example 1.

Example 4 Electrolysis is effected with the same electrolyte as described in Example 3 with the use of lead anodes and a temperature of 70 C. A molten mixture of 156 grams of sodium aluminum triethyl fluoride and 166 grams of sodium aluminum tetraethyl which is equivalent to the amount of current passed through is allowed to flow in per 26.8 amps. hours. A current density of a./dm. is obtained with a terminal voltage of 5 v. Pure tetraethyl lead separates from the electrolyte, collects at the bottom of the electrolytic cell and may be withdrawn from time to time. Withdrawn from the electrolytic cell is a continuous stream of 270 grams NaF.2Al(C H per 26.8 ampsxhours. This is freed from dissolved tetraethyl lead by washing with octane at 20 C. The lead-free compound is mixed with 24 gms. of NaH per 270 grams and heated to 100 C. while stirring. The NaH dissolves completely. The resultant reaction mixture of 156 g. of NaAl(C H F and 138 g. of NaAl(C I-I H is treated with ethylene at 150 C. and a pressure of 20 atmospheres until a pressure drop does no longer occur. The resultant reaction mixture of 6 g. of NaAl(C H F and 166 g. of sodium aluminum tetraethyl may be returned into the electrolytic cell.

Upon processing of the octane solution of tetraethyl lead and combination with the directly separated Pb(C I-I tetraethyl lead is obtained in amount of 79 g. (corresponding to 98% of the theory) per 26.8 amperesxhours.

Regarding the sodium amalgam, the procedure is the same as that described in Example 1.

Example 5 The procedures is the same as in Example 1 except that a Mg anode is used. Formed at the anode is a compound of the composition Mg(C H .2Al(C H which, since sparingly soluble, separates as the upper layer which can be withdrawn. When heating this layer at 100 C. under a vacuum of 10* mm. Hg, almost all of the aluminium triethyl distils off. The distillation residue is suspended in dry pentane and the insoluble magnesium diethyl is separated from pentane used for washing by centrifuging. The solid deposit is dried in a high vacuum of 10 mm. Hg and at 80 C. after having decanted the Pentane. There is obtained aluminum-free magnesium dilti ethyl in amount of 39 g. (corresponding to 96.5% of the theory) per 26.8 amps. hrs.

Example 6 The electrolyzer consists of a simple heatable cylindrical vessel containing at the bottom mercury in the form of a layer of, for example, 1 to 2 cm. depth. Molten sodium aluminum tetraethyl is filled above the mercury. Immersed in this electrolyte is a bundle of indium plates arranged vertically at a small distance. The thickness of the plates may be, for example, about 2 to 3 mm. and their distance is about 2 mm. The arrangement of plates is advantageous because small amounts of gases are evolved at the anode during the electrolysis which may easily escape upwardly through the interspaces. The bundle is approached to the mercury leaving a distance of a few millimeters. The electrolysis is effected at a terminal voltage of 4 v. and current densities of 15 a./dm. at an electrolysis temperature of 125 C. The bundle of plates dissolves beginning with the lower edges. The mercury converts into a sodium amalgam of gradually increasing concentration and a mixture of indium triethyl and aluminum triethyl collects at the surface of the electrolyte layer. This mixture may be withdrawn intermittently or continuously. Molten sodium aluminum tetraethyl at a rate of 166 g. per 26.8 amps. hrs. which is equivalent to the current passed through is allowed to flow into the electrolytic cell. If the sodium concentration in the mercury reaches about 0.3%, the amalgam must be removed from the electrolytic cell intermittently or continuously and replaced by amalgam of lower sodium content. The sodium amalgam, in a secondary cell, is freed electrolytically from sodium except for a small residual content of about 0.1% and may subsequently be reused as the cathode.

The mixture obtained of indium triethyl and aluminum triethyl is separated into indium triethyl (distillate) and aluminum triethyl (distillation residue) at a temperature of 42 C. (measured in the vapors) and a vacuum of 0.6 mm. Hg. The aluminum triethyl is reacted with NaH and ethylene under a pressure of 20 atmospheres and at 180 C. and thereby reconverted into sodiumaluminum tetraethyl. The yield of indium triethyl is 58 g. per 26.8 amps. hrs. (corresponding to 86.5% of the theory).

Example 7 The procedure is the same as in Example 6 except that plates of antimony are used as the anodes. The mixture obtained of antimony triethyl and aluminum triethyl is heated at 90 C. (measured in the liquid) in a vacuum of 15 mm. Hg. In doing so, the antimony triethyl distils completely. The distillate contains small amounts of aluminum triethyl. The antimony triethyl may be purified by a simple steam distillation since Sb(C H does not react with water. The yield of Sb(C H is 70 gms. per

. 26.8 amps. hIs. corresponding to 100% of the theoretical yield.

Attention should be paid to the fact that due to the sensitivity of the electrolytes and most of the reaction products to air and water all operations must be carried out with exclusion of moisture and under an inert atmosphere such, for example, as nitrogen or argon.

Example 8 The electrolysis is effected in the apparatus described in Example 1 using a mixed electrolyte consisting of 50 mol-percent potassium-aluminum tetraethyl and 50% so- 17 a bath temperature of not more than 90 C. in the distillation.

The yield of Sn(C- H is 50 g. per 26.8 amps. hrs. (corresponding to 85% of the theoretical yield).

Example 9 The procedure is the same as in Example 8 except that thallium is used as the anode. Care should be taken during the electrolysis that the sodium concentration in the mercury does not exceed 0.1 to 0.15%. Part of the about 0.15% amalgam is withdrawn from the electrolytic cell and replaced by pure mercury.

The sparingly soluble lower phase of thallium triethyl and aluminum triethyl isheated at 60 to 65 C. (measured in the liquid) in a vacuum of 10 mm. Hg. In doing so, Tl(C H distils and aluminumutriethyl is left as the distillation residue.

The yield of Tl(C H is 85 g. per 26.8 amps. hrs. (corresponding to 88% of the theoretical yield).

Example 10 The procedure is the same as described in Example 8 except that bismuth is used as the anode. The electrolysis is effected until the sodium concentration in the mercury is about 1% whereafter the sodium amalgam is replaced by pure mercury or an amalgam of lower sodium content. The mixture obtained of bismuth triethyl and aluminum triethyl which is sparingly soluble in the electrolyte is separated by distillation at 1 mm. Hg. Bismuth triethyl distils at 48 C. (measured in the vapors) and aluminum triethyl is left as the distillation residue. The yield of bismuth triethyl per 26.8 amps. hrs. is 89 g. (corresponding to 89% of the theoretical yield).

Example 11 The production of mercury diethyl is advantageously effected with the following simple setup: The outer vessel may, for example, be constituted by the glass cylinder described in Example 6 and used for operation with solid metal anodes. The body of mercury which, at the bottom ofthe vessel, is contained in a glass cylinder of about 2 cm. in height is subdivided into an inner mercury body of circular cross section and an outer mercury body of annular cross section by inserting a second vessel (of insulating material, e.g. glass). The mercury in the inner vessel is at a somewhat higher level than the outer mercury, is insulated from the latter and is used as the anode. The outer mercury ring is used as the cathode. Running at a small distance above the mercury surface is a stirrer which continuously renews the electrolyte above the surface. The diameter of the outer glass cylinder is preferably chosen a few centimeters greater than that of the outer mercury container so that quiescent zones free from flow are able to develop in the electrolyte in this area in which the sparingly soluble second phase of mercury diethyl and aluminum triethyl is capable of settling and being removed intermittently or continuously.

The electrolysis is effected with a mixed electrolyte consisting of 70 mol-percent of KAl(C H) and 30 molpercent of NaAl(C H using a temperature of 80 C. and adding molten NaAl(C H at a rate which is equivalent to the current passed through. The sodium amalgam deposited at the cathode is replaced by an amalgam of lower sodium content or by mercury not later than after having reached a Na content of 1.3%. The mixture of mercury diethyland aluminum triethyl obtained as the. second phase is heated at 60 C. in a vacuum of 1 mm;

Hg. In doing so, all of the mercury diethyl distilswhile um hydride was dissolved.

mercury-free aluminum triethyl is obtained as the distillation residue.

The yield of Hg(C H is 120 g. per 26.8 ampsxhrs. (corresponding to 93% of the theoretical yield).

vessel with a ground rim, which could be tightly closed with an aluminum cover. This cover had two simple bore holes fora thermometer and the current supply for the mercury cathode, a connection for an inert safety gas and a bushing for the lead anode, which simultaneousl-y served as stirrer for the electrolyte. The lead anode was in the form of a lead disc 15 mm. thick provided with numerous lateral stirring blades. The anode stirrer had a hollow shaft through which a glass stirrer for the mercury extended. The glass stirrer was rotated at a velocity of 10 r.p.m., vhilc the lead anode was moved at a rate so that the mercury would just remain at rest at an electrode distance of 12 mm. The cell was heated through an oil bath. The strong stirring of the electrolyte was necessary since otherwise the lead tetraethyl formed would settle as specifically heavy second phase on the mercury cathode and would interrupt the current-flow between cathode and anode. By stirring the lead tetraethyl remained suspended in the electrolyte.

The cell was filled under inert gas with 180 ccm. (about 2.5 kg.) mercury and the electrolyte, which consisted of 320 g. (1.753 mol) potassium-aluminum-tetraethyl and 91 g. (0.528 mol) potassium-aluminum-triethylfluoride and heated to A direct current was then applied which, with a resistance, was regulatedto a constant current flow of 5 amperes.

The oil-bath temperature, during the entire run, was 85. With an anode surface of 27 cm?, the current density amounted to 18.5 amperes/dmF, with a voltage of 3.8 volts.

After the finish of the run, the electrolyte was siphoned off. The weight loss of the lead anode amounted to 19.0 g., i.e. 98.5% of the theory.

The potassium amalgam recovered weighed. 2460 g. and contained in all 14.7 g. potassium, that corresponds. to the theoretical quantity of 14.6 g.

The entire electrolyte was heated for two hours at 10" torr to and 29.5 g. of a colorless liquid distilled off which was identified. through analysis as pure tetraethyl lead, leaving the electrolyte free of detectable quantities or" lead. For the regeneration, the electrolyte was stirred with 0.375 mol NaI-I at 100 C. until all sodi- The sodium hydride was charged in the form of a l020% suspension in mineral oil. The oil which is not miscible with the electrolyte settles after the reaction as upper layer. The clear melt, separated from the oil, was thereupon filled into an autoclave and treated at about 175 and 15 atmospheres with ethylene. After 3 hours the ethylene absorption ceased. A confirmation, therefore, that after this time the ethylene-addition was finished, was given by the analysis of the alcoholysis gas which did not contain. any more. hy

drogen (composition: 1.5% n-C H 97.9% C H 0.6%

(1 111 The reaction product was then stirred for 5 minutes at 100 with an equivalent quantity potassium amalgam which contained 0.6% potassium. In the melt separated from the amalgam, sodium could no longer be detected even through the flame coloration.

Example 13 An apparatus corresponding to that shown in FIG. 1. is used but which is additionally equipped with a descending cooler and a distillationreceiven The cell is equipped with lead anodes and NaAMCH M-melt as the electrolyte. A. current density of 50 a./dm. is maintained through a terminal voltage of 1.5 volts. Equivalent to the passed through, current quantity, g. NaAl(CH per 26.8 amperehour is. allowed to flow into the cell. The anodically formed mixture of Pb(CH and Al(CH distills off from the electrolysis cell at the electrolysis-temperature immediately after formation and is collected in, the distillation received. The cathodically formed Na-amalgam is continually removed and in asecondarycell sodiurn is recoveredfrom the amalgam in known manner.

l 19 The amalgam poorer in sodium is continually again returned to the cell.

What is claimed is:

1. A process for producing an alkyl of a metal selected from the group consisting of beryllium, magnesium, mercury and metals of main groups III to V of the periodic table by electrolysis of aluminum-organic compounds, which comprises subjecting compounds of the general formula Me[AlR R] wherein R is an alkyl radical, R

is a member selected from the group consisting of alkyl, alkoxy and cycloalkoxy radicals and fluorine, and Me is a metal selected from the group consisting of sodium, potassium and mixtures of sodium and potassium, to electrolysis at current densities in excess of 2 a./dm. with the use of anodes of the metal Whose alkyls are to be produced and a mercury cathode.

2. A process according to claim 1, wherein compounds containing the same alkyl radicals are used.

3. A process according to claim 1, wherein use is made of an electrolyte which additionally contains a compound of the general formula AlR R wherein R is an alkyl radical and R is. a member selected from the group consisting of alkyl and alkoxy radicals.

4. A process according to claim 3 wherein an etherate of said aluminum triallcyls is used.

5. A processaccording to claim 3 wherein a trialkyl aminate of said aluminum trialkyls is used.

6. A process according to claim 1, wherein use is made of compounds of the general formulae given above wherein R is a straight chain primary alkyl radical containing up to 6. carbon atoms, R is a member selected from the group consisting of straight chain primary alkyl radicals containing up to 6 carbon atoms, alkoxy radicals of the general formula OR" containing up to carbon atoms, and fluorine, and Me is a metal selected from the group consisting of sodium and mixtures of sodium and potassium containing up to about 80% of potassium.

7. A process according to claim 1, wherein a compound of the general formula selected from the group consisting of MeAlR MeAlR OR", NaF.AlR NaF.2 AlR and mixtures thereof are used as the electrolyte.

'8. A process according to claim 1, wherein anodes of a metal selected from the group consisting of magnesium, mercury, aluminum and lead are used.

9. A process according to claim 1, wherein the metal alkyl compound produced from the anode metal is separated by distillation from the aluminum-containing decomposition products of the electrolyte.

10. A process according to claim 9, wherein said distillation is a vacuum distillation.

11. A process according to claim 1, wherein the metal.

alkyl compound produced from the anode metal is separated from the aluminum-containing decomposition products of the electrolyte by separation into layers.

12. A process'according to claim 1, wherein said electrolysis is effected until the Me concentration in the Me amalgam formed is about 1.5% by weight and the amalgain is withdrawn from the electrolyzer.

13. A process according to claim 1, wherein the Me amalgam removed from the electrolytic cell is at least partially freed from its Me content to recover the mercury.

14. A cyclic process for the production of metal alkyls according to claim 1, which comprises subjecting an electrolyte containing at least one of the compounds of the general formulae Me [AlRgR and AlR R' [to electrolysis with the use of anodes consisting of the metal whose alkyls are to be produced and a mercury cathode, continuously removing the resultant Me amalgam from the electrolysis vessel; freeing said amalgam at least partially from its Me content in a second electrolysis and returning it into the primary electrolysis for the production of metal alkyls while the metal alkyls formed and the aluminum-containing decomposition products of the electrolyte are separated from the electrolyte and separated from each other, whereupon the aluminum-containing decomposition products, together with the metal Me from the secondary electrolysis of the Me amalgam, are treated outside of the electrolyzer with hydrogen and olefins to be reconverted into the electrolyte compounds decomposed during said electrolysis and are returned in this form into the primary electrolysis.

' 15. A cyclic process for the production of a metal alkyl according to claim 1, wherein said electrolysis is effected with an electrolyte containing the compounds NaF.AlR (1:1 compound) and NaF.2AlR (1:2 compound), and portions of theelectrolyte are withdrawn and freed from the metal alkyl compound formed from the anode metal whereupon the 1:2 compound is treated outside of the electrolyzer with sodium, hydrogen and an olefin to form the 1:1 compound and the compound of the formula NaAlR at the rate at which the 1:2 compound was formed from the 1:1 compound during the electrolysis, whereupon the electrolyte thus treated is returned into the electrolytic cell. I

16. A process according to claim 1, wherein current densities from 5 to about amperes/dm. are used.

17. A process according to claim 1, wherein temperatures from about 100 to about C. are used.

18. A process according to claim 1, wherein terminal voltages of about 1 to 5 volts are used.

19. A process according to claim 1, wherein electrode gaps between the anode and cathode of a few millimeters are used.

20. A process according to claim 1 in which said anode metal and R are selected to form metal alkyls which are lighter in weight than the electrolyte and in which use is made of an anode which contains the metal to be converted into the alkyl compound in the form of a bundle of plates having sufficiently wide interspaces between the individual plates that the formed metal alkyl and small amounts of gaseous reaction products evolved anodically are capable of migrating in upward direction between the plates.

21. A process according to claim 20, wherein said interspaces between said individual plates of said bundle of plates are a few millimeters.

22. A process according to claim 1 in which said anode metal and R are selected from metal alkyl compounds descending in the electrolyte and in which use is made of a flowing electrolyte such that the electrolyte flowing over the mercury surface entrains the descending metal alkyl compound which descends to the bottom in a part of the apparatus which is substantially free from flow.

23. A process according to claim 1, wherein said electrolysis is eifected in vacuo.

24. A process according to claim 1 for the production of tetraethyl lead in which said anode is lead, in which R is an ethyl radical.

25. A process according to claim 1 for the production of tetramethyl lead in which said anode is a lead anode, in which R is a methyl radical.

26. A process according to claim 1 in which said compound of the general formula comprises a mixture of potassium-aluminum-tetraethyl and potassium-fluoridealuminum-triethyl complexes.

27. A process for the electrolytic production of an alkyl of a metal selected from the group consisting of mercury, and metals of main groups II to V of the periodic table by electrolysis of aluminum-organic compounds which comprises passing an electrolysis current between an anode of the metal whose alkyls are to be produced and a cathode of mercury, through an electrolyte comprising a mixture of potassium-aluminum-tetraalkyl and a potassium-fluoride-aluminum-trialkyl complex to thereby form'a mixture of potassium-aluminum-tetraalkyl, potassium dialuminumhexaalkylfiuoride and the metal alkyl and recovering the metal alkyl.

28. A process according to claim 27 in which said elec- 431 trolyte is a mixture of said aluminum compounds which contain lower alkyl radicals.

29. A process according to claim 27in which said aluminum compounds contain ethyl radicals.

30. A process according to claim 27 in which said electrolyte comprises a mixture of potassium-aluminum-tetraethyl and potassium-aluminum-triethylfiuoride, and in which the electrolysis is effected until a substantial portion of said potassium-aluminum-triethylfluoride has been converted .to potassium-dialuminum-hexaethylfiuoride.

31. A process according to claim 30 in which the electrolyte contains 0.43-0.18 mols of potassium-aluminumtriethylfiuoride per mol of potassium-aluminum-tetraethyl.

32. A process according to claim 27 in which the electrolyte comprises a mixture of potassium aluminum-tetraethyl and potassium-dialuminum-hexaethyliiuoride.

33. A process according to claim 32 which includes continuously removing electrolyte containing tetraethyl 2.22 lead from the cell and recycling electrolyte to the cell to maintain the composition of the electrolyte substantially constant.

34. A process according to claim 27 in which the formed .tetraethyl lead is removed from the electrolyte by settling and residual tetraethyl lead removed by vacuum distillation 35. A @rocess according to claim 27 in which a content of potassium-aluminumdetraQethyl is maintained in the electrolyte sufficient to maintain the melting temperature of the electrolyte below about 100 C. and in which the electrolysis is efiected at a temperature between about 70 and 100 C.

References Cited in the file of this patent UNITED STATES PATENTS 2,849,349 Zeigler Aug. 28, 1958 2,944,948 Giriatis July 12, 1960 2,985,568 Zeigler May 23, 1961 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,164,538 January 5, 1965 Karl Ziegler et a1.

It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 2, line 40, for "Where" read When column 6, line 37, for "Process" read Processes column 7, line 9, for "olefins" read olefin column 10, line 35, for "mol" read mols lines 40 and 41, for "produce" read produc column 17, line 59, for "KAl(C H) read KAl(C H 2 4 2 5 4 column 20, line 65, for "II to V" read III to V Signed and sealed this 15th day of June 1965.

(SEAL) Attest:

ERNEST W. SWIDER EDWARD J. BRENNER Attcsting Officer Commissioner of Patents 

1. A PROCESS FOR PRODUCING AN ALKYL OF A METAL SELECTED FROM THE GROUP CONSISTING OF BERYLLIJM, MAGNESIUM, MERCURY AND METALS OF MAIN GROUPS III TO V OF THE PERIODIC TABLE BY ELECTROLYSIS OF ALUMINUM-ORGANIC COMPOUNDS, WHICH COMPRISES SUBJECTING COMPOUNDS OF THE GENERAL FORMULA ME(AIR3R'') WHEREIN R IS AN ALKYL RADICAL, R'' IS A MEMBER SELECTED FROM THE GROUP CONSISTING OF ALKYL, 